1. Field of the Invention
The invention pertains to vehicle torque box chassis frames for supporting extendible aerial ladders, such a frame being particularly useful with firefighting vehicles.
2. Description of the Related Art
Firefighting vehicles such as ladder trucks include extendible aerial ladders whereby the ladders may be raised and extended in excess of one hundred feet, as may be required in fighting fires in multiple story buildings, or conducting rescues therefrom.
Commonly, extending aerial ladders are hydraulically operated whereby the ladder assembly may be lowered to a stored position, and raised to an operative position. The ladder system consists of a plurality of extension ladders, and when the ladders are extended, and partially raised, significant bending forces are applied to the frame of the support vehicle due to the weight of the ladders, and any personnel or equipment supported thereon.
In order to stabilize vehicles supporting extendible ladder systems, it is common to mount jack systems upon the vehicles which extend laterally from the vehicle sides and include hydraulically extendible jacks for engagement with the ground to stabilize these vehicles during ladder extension. Most jack systems are attached to the conventional vehicle structure, including the suspension system, and while such jack systems do greatly improve the vehicle stability during aerial ladder extension due to the high centroidal moment of inertia imposed upon the vehicle by an extended aerial ladder, the ultimate degree of stability desired has not been achievable, and the height of extendible aerial ladders has been limited due to the inability to provide as stable a ladder platform as possible.
Efforts have been made to improve the stability of aerial ladder platforms as formed on firefighting vehicles, as shown by the assignee's U.S. Pat. No. 4,570,973. In this patent an elongated torque box of generally rectangular transverse cross section utilizes a plurality of braces and webs to form a substantially rigid elongated box upon which the aerial ladder may be supported. However, due to limitations in the vertical dimensions of the torque box shown in U.S. Pat. No. 4,570,973, and structural limitations due to the relationship of the ladder supporting structure to the remainder of the torque box, optimum ladder supporting characteristics were not achieved.